A damper provides a damping force in reaction to motion. A damper is typically filled with a damping fluid to provide fluidic resistance to the motion of a piston traveling through the damping fluid. A conventional piston generally includes valves for compression flow of damping fluid and valves for rebound flow of damping fluid. In this regard, shims are used to block one set of valves during each motion of the piston. For example, if the damper is experiencing a compression stroke, the rebound valves are blocked by the rebound shims. Conversely, when the damper is in a rebound stroke, the compression valves are blocked by the compression shims.
Shim configuration can greatly impact the performance and damping characteristics of the damper. Generally, a combination of different thicknesses and sizes of shims (referred to as a “shim stack”) is used to tailor the characteristics of the damper during use. Shims are typically metallic discs that are capable of bending with a low rate of fatigue. In this regard, spring steel is often a material used for the shims. When the damper is in a compression stroke, and the rebound valves are blocked by the rebound shims, the compression shim stack is necessarily bent away from the compression valves to allow flow of the damping fluid through the piston. The rate of the flow determines the damping force. If the compression shim stack allows freely flowing damping fluid through the compression valves, the damping effect will be small. If the compression shim stack greatly restricts flow of damping fluid through the compression valves, the damping effect will be high.
Given the influence of the shim stack on the performance and damping characteristics of the damper, the shims are often configured in a manner that provides consistent and repeatable damper performance. The damper can be tuned by adjusting the shim stacks. In one configuration, a shim stack can be preloaded such that the shims do not bend to allow flow through the piston valves until a certain damper speed is reached. In this regard, the low speed travel of the damper has a higher damping force before the shim stack bends to allow flow through the piston valves. A variety of configurations for preloading the shim stack exist in conventional dampers. In one example, a digressive piston is used to apply a preload to the shim stack. Digressive pistons can be expensive and require very specific installations to perform as desired. Another configuration to preload the shim stack is to use a ring shim. In this type of preload configuration, the ring shim is positioned within the shim stack to bend, or preload, the shim stack. Often the ring shim can become misaligned, giving inconsistent performance characteristics for the damper.
Therefore, a need exists for an improved preloaded shim stack configuration that eliminates the performance inconsistencies of the damper, without using a digressive piston. Embodiments of the present disclosure are directed to fulfilling these and other needs.